Circuit interrupter



. ug- 3, 1943. J. sLEPlAN 2,326,074

- CIRCUIT INTERRUPTER Filed Sept. 20, 1939 5 Sheets-Sheet i?.

'..a'zaurannurr wfg Aug, 3 E943.

J. LEsQaAN 2,3%?@74 CIRQUE INTERRUPTER Filed sept. 2o, 1959 3 sheets-sheet '5 f1 JKL 22.1' f

zsulalian wlTNEsss: am M 87.9 INVENTOR 07m 186,/ Josgm gam.

Patented Aug. 3, y1941i CIRCUIT INTERRUPTER Joseph siepien, Pittsburgh, Pa., assigner te west,- inghouse Electric- Manufacturing Company,

a corporation of Pennsyl- East Pittsburgh, Pa., vania f Application september zo, 1939, serial No. 295,727 ancienne. (c1. zoo-144)` My invention relates to apparatus involving arc discharges and has particular relation to circuit interrupters in which a short arc is produced when the contacts are disengaged.

In circuit interrupters constructed in accordance with the teachings of the prior art, difficulty is encountered because the contacts are excessively heated. For a semi-infinite solid (which is a solid extending indenitely in one direction) having specific heat c, thermal-conductivity k, density the rise in temperature T of the surface is given by If 7111.194155 t 10:1, 0:1516, 6:8 In such a case, Y

If the arc burns for 1/2 period of an ordinary 60 cycle source, t==$g and T=2800 C. Thus, the surface of a copper electrode functioning as the cathode fo'r an arc in air is raised to a temperature substantially above the boiling pbint of the copper, even if the arc burns for only 1/2 period of a 60 cycle source.

In accordance with the teachings of the prior art, the heat developed by the arc may be dissipated by magnetically moving-the arc over the electrode surface. However, the apparatus required for the movement and the cooling of the arc is relatively complex and considerable expense is involved in its construction and maintenance.

It is accordingly an object of my invention to provide a reliable circuit interrupter of simple structure. l

Another object of my invention is to provide a circuit interrupter in which an excessive rise 'in temperature shall not occur when the contacts are disengaged.

A further object of my invention is to provide a circuit interrupter, the operation of which is .dependent on the ignition of a short arc when the contacts are deenergized that shall function satisfactorily without the aid of the usual arc moving and cooling mechanisms.

A more general object of my, invention is to provide an arrangment for use in circuit interrupters or in lightning arresters in which the ignition of an arc shall not result in the development of excessive heat.

A more specific object ,of my invention is to provide a circuit interrupter of simple structure for use in interrupting high potentials.

Another specic object of my invention is to provide a circuit interrupter of the vacuum type in which the force required to actuate the contacts shall he relatively small.

More specifically stated, it is an object of my invention to provide simple and inexpensive arc interrupting means for use in circuit breakers, commutators, lightning arresters, andthe like.

My invention arises from the discovery that the heat concentration developed at the cathode of an arc is relatively small when the arc is operated in a gaseous atmosphere at a pressure of the order of several centimeters of mercury.

` Specifically, I have found that the pressure in which the arc is burning should be of the order of 1 cm. for the most propitious results. However, a material improvement over arcs operating atv atmospheric pressure or in high vacua is manifested by an arc operating at a pressure as high as 10 cm., on one hand, and as low as .1 cm. on the other hand. When the pressure is lower than .1 cm. difculties arise because the arc becomes concentrated over small areas of the electrodes.

In accordance with my invention, I provide a circuit interrupter in which the contacts are disposed in a gaseous medium at a pressure of the order of several centimeters of mercury. The contacts are disposed in a vacuum tight container in which the pressure is of the desired magnitude. The container is provided with a movable wall and the movement of the contacts isv effected by moving the wall. My invention is particularly applicable to short arc structures and for this reason, the distance between the contacts of the interrupter when they are open is preferably of the order of .1 cm.

I have found moreover that the energy developed at the contacts may be materially decreased by properly selecting the attenuated gas in which the contacts operate. The current density I of a cold cathode arc I believe is given by where K is a constant, P is the pressure of the gas, E1 is its ionizing potential, and M is its molecular weight. If gases having a low value of M are selected the current density is materially reduced. Noble gases such as helium, argon, xenon,

krypton, and nitron have substantially lower values for than ordinary gases. Thus, for xenon the value is .1, while it is 74 for nitrogen and .39 for oxygen. In accordance with my invention therefore the gas within the vacuum tight container is preferably a noble gas such as xenon.

Since the contacts in a circuit interrupter constructed in accordance with my invention aremaintained in a relatively low pressure medium,

atmospheric pressure has a material eiect on the l cuit interrupter and the mechanism for moving the contacts that the volume of the container remains substantially constant when the contacts `are moved..

is Because of the short arc ignited in a circuit iterrupter in accordance with my invention, the potential rating of a single'interrupter is small. Where substantial potentials are to be interrupted, a plurality oi individual sets of contacts are connected inv series. The contact may be disposed in a tank containing an insulating liquid such as oil and the operation may take place by com-v A pressing and relaxing the liquid.

In accordance with a still further aspect of my invention, the commutators of an energy converting arrangement are operated in a medium at a pressure of the order of several centimeters of mercury and arcs are produced between the brushes and the commutator segments when the segments are disengaged from the brushes. Since the energy density at the electrodes generated by the arcs is relatively small, the commutators are not deleteriously aiected by the arcs and the rating is materially higher'than that for equivalent apparatus designed to operate in air. To further improve the energy conversion arrangement readily saturable chokes may be connected in series with the commutator segments. The` chokes of the type preferably used in thepractice of my invention saturate at a current of the order of several amperes. Accordingly, during commutation when the current is relatively low, the

chokes offer a high impedance to the current iiow and decrease the energy developed in the regions in which segments and brushes are separating. When the current is equal to the normal load current, the chokes are saturated and oier substantially no impedance to the current oW.

The nove1 features that I consider characterise tic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its methdpf operation, together with additional objects and advantages thereof, will best be understood from the following description of speciiic embodiments when read in connection with the accompanying drawings, in which:

Figure 1 is a view in top plan of a circuit inter-A VI-VI of Fig. 5;

Fig. '7 is a view in section showing a high voltage circuit interrupter in accordance with my invention;

Fig. 8 is a view in top plan of another modification of my invention;

in Fig. l2; and

Fig. 14 is a diagrammatic view showing another converting arrangement in accordance with my invention.

The apparatus shown in Figs. l and 2 comprises a short cylindrical container I5 formed by composite upper and lower plates I1 and I9, respectively, and an insulating ring 2I between the plates. The upper plate I'I is made up of a central disc 23 of an ordinary metal, such -as steel,

and a concentric ring 25 of an alloy which forms a vacuum-tight seal with an insulator, such as glass. The ring 25 may, with advantage, be composed of an iron-nickel-cobalt alloy, sold under the trade name Kovar. The lower plate I9 is made up of a central disc-shaped, flexible diaphragm 2'I and a concentric alloy ring 29 similar to the upper ring 25.

The alloy rings 25 and 29 are welded to the disc 23 and the diaphragm 2l in such manner that the joints are vacuum-tight. The insulating ring 2l is preferably composedof a glass, which seals to the alloy of which the rings 25 and 21 are composed, and is sealed to the rings. The glass is preferably Corning,.G705-`AJ or G-704-AJ. The disc 23 is provided with an outlet tube 3D through which the container is exhausted to a pressure of the order of 1 cm. of mercury and which -is thereafter sealed off. Since the seals and the welds are vacuum-tight, the low pressure is` maintained indefinitely. Contacts 3l and 33 are welded at Athe centers of the disc 23 and the diaphragm 2l. The thickness of the insulating ring 2I is such -that the distance between the contacts 3I and 33 when they are open is of the order of .1 or .2 centimeter. With the contacts so close together the contact surfaces are available to condense the ionized gases which arise in the ignition of an arc when the contacts are separated.` However, under certain circumstances this advantage may not be necessary and the broad aspects of my invention may be practiced with the distance between the contacts 1 cm. or more.

The `contacts 3| and 33 areclosed by moving the diaphragm upwardly and thus causing the contact 33 on the diaphragm to engage the one The movement ofthe through the cooperation of a spiral-shaped peripheral cam 35 and a cam follower 31 extending from the diaphragm. 'Ihe follower 31 is a metallic plate in the form oi'- a truncated right triangle with the narrow end engaging the cam 35. As the cam 35 is rotated in a counterclockwise direction from the position shown in the drawings, it raises the follower 31 and the diaphragm 21 and its contact 33 against the resilient force exerted by the diaphragm and urges the contact 33 into engagement with the contact 3|. When the cam is rotated in the opposite direction, the contacts 3| and 33 are disengaged bythe restoring force exerted by the diaphragm. The contacts 3| and 33 maybe connected in a circuit by terminals 33 and 4|, respectively. The former (33) is secured to the disc 23 and the latter (4|) carries a brush I3 which engages the vertical side of the cam follower 31.

The above-described apparatus may be used with advantage in cases in which an alternating potential of the order of 200 to 400 volts R. M. S. is to be interrupted. The current density of the arc at the pressure in the container l is relatively low and, therefore, the heat produced is not such as to deleteriously affect the contacts 3| and 33 when they are disengaged.

In Fig. 4, the relationship between the pressure and the current density at the cathode of an arc is shown graphically. Pressure is plotted horizontally, and current density vertically. As can be seen from the curve 55, the current density is relatively high for pressures of the order of one atmosphere or more. As the pressure is decreased, the current density decreases until it approaches a minimum in the region of pressures of the order 'of one centimeter of mercury. As the pressure is now further decreased, the eurrent density increases, and for low pressures approaches the values that it has at one atmosphere. In accordance with my invention, the pressure is maintained at approximately one centimeter of mercury and, therefore, the energy consumed at the cathode when an are is ignited between the contacts is relatively small.

While the energy developed in the arc produced on the opening of the contacts of an interrupter constructed in accordance with my invention is relatively small, the temperature is raised materially. The rise in temperature does not affect the contacts, but may affect vthe insulating ring 2|. This undesirable condition is remedied in accordance with a further aspect of my invention by using a laminated insulating ring 41, as shown in Fig. 3, in lieu of the homogeneous structure 2| of the Fig. 2 arrangement. In the Fig. 3 structure the insulating ring 41 is formed of a series of thin glass rings 43 with alloy laminations 5| interposed. 'I'he alloy rings prevent the deterioration of the insulation by the heat developed. y

While the laminated insulator has substantial advantages in a switch of the type disclosed herein, its most important function arises in connection with lightning arresters constructed in accordance with my invention. In apparatus of the latter type, an arc is ignited between opposite walls voi a region maintained at a pressure of the order of one centimeter` when a high potential is impressed on the lapparatus protected. The arc has a tendency to move towards the boundary of the region where the insulation is located, and may excessively heat the insulation. When the a container 53 formed by a flanged hollow cylinder 55 from the center of one base of which a reentrant hollow cylinder 51 is suspended, and a resilient shell 53 ot horizontal C section welded to the ilange 6| of the cylinder 55. The reentrant cylinder has a wall of composite structure comprising a pair of alloy rings 33 and 35 separated -by a glass ring 81. The upper alloy ring 33 is welded -to an annular tip 33 extending downwardly from the base of the flanged cylinder 55, and the lower ring 35 is welded to a disc 1|. The disc 1| and the cylinder 55 may be composed of a metal, such as steel. Contacts 13 and 15 are welded to the disc 1| and the base of the shell 53, respectively. The height of the shell is such that when the contacts 1| and 13 are disengaged the distance between them is of the order of .l centimeter. The container is evacuated to the same pressure as the corresponding containers in the apparatus shown in Figs. 2 and 4. As in the latter apparatus, contacts 13 and 15 are engaged by the cooperation of a cam 35 and a cam follower 31 which cause the base of the shell 53 to move upwardly. In the apparatus shown in Figs. 2, 4 and 6, the resilient shell or diaphragm should be composed of relatively stiif material since the force, exerted on its surface by reason of atmospheric pressure, is relatively large. In general, the material of which the diaphragm or shell is vcomposed may be constructed of suiliciently heavy material to accomplish this purpose. If the heavy material is i'or one reason or another not desired, separate springs may be used to supply the necessary force.

Where a higher rating is required than the several hundred volts of which the units shown in Figs. 2, 4 and 6 are capable, a system of the type shown in Fig. 7 is used. In this arrangement a plurality of circuit interrupters 11 are connected in series. Each interrupter comprises a container 13, the walls of which are a solid composite plate 3|', and an annular composite plate 83 closed by a Sylph'on 85 extending from the center, and an insulating ring 81 between the plates. The solici plate 8| is made up of a solid disc 83 of any suitable metal, such as steel, to which a Kovar alloy ring 3| is welded. The annular plate 83 is made up of an annular disc 33 of steel or other suitable metal and alloy ring 35. The Sylphon 85 is provided with a flanged opening and the flange 31 is welded to the annular disc 33. 'Ihe insulating ring 81, which may -be composed of glass, is sealed between the alloy rings 3| and 35. The containers 13 are exhausted to the same pressure as the containers in the other modifications of my invention.

The contacts 33 and ||l| of the interrupters 11 are secured to the center of the solid disc the base of the Sylphon 85, respectively. The contact |3| is coaxial with the sylphon 85 and extends along its length to apoint such that when it-is disengaged from the contact 33, the distance between the contacts is of the order of .l centimeter. The interrupters 11 are connected in series by U- 83 and containers 1S.

The interrupters il, together with their connecting brackets |63, are disposed in a vessel m lled with an insulating liquid, such as oil. The

vessel is provided with terminals Mil and |99 to which the outside plates 3| and 83, respectively, of the interrupters on the ends of the assembly areY connected through L-braclrets welded to the plates. l

From one end of the vessel` d, a cylindrical tube ||3 extends and a piston is slidably disposed in the tube. rlire piston ||i is secured to a rod |1 which is coextensive with the armature H9 oi' a solenoid |2i. 'When the solenoid |2| is energized, the rod ||l is moved downward against the action of a compression spring |23, which engages a disc |25 secured to the rod and the top of the cylinder H3, and the liquid is compressed. The pressure exerted^ by the piston H5 is transferred through the liquid to the Sylphons 35 and the contacts 93 and ||l| are closed. The contacts are maintained closed by the engagement of a latch |211 with one end oi' a lever |23, the other end of which is pivotally secured to the rod H1. The lever is rotatable about a xed pin |3| intermediate its ends and is rotated upward about the pin |3| into engagement with the latch |271 when the closing solenoid |2| is energized. vThe latch |2'i may be disengaged from the lever |29 by energizing an opening solenoid |33. Under such circumstances, the piston H5 moves upwardly under the action of the spring |23 and the contacts are opened.

The hydraulic actuating mechanism is, of course, not the only arrangement which can be used to actuate a plurality of interrupters in accordance with my invention. For example, the movable contacts 99 and |9| may be actuated by a lever mechanically coupled 'to all of the Sylphons. As is the customary practice, the lever, may be latched in the closed position and the latch released when the circuit interrupter is to be opened.

In Figs. 8 and 9, a modification of my invention is shown in which the contacts are operated without changing the volume of the evacuated containers.- Because the volume is maintained constant, the eilect of atmospheric pressure is eliminated, and the heavy resilient elements in the modifications discussed heretofore may be replaced by relatively light springs.

The apparatus comprises a container |35, the walls of which are a composite yupper plate |31, a homogeneous lower plate |39, an insulating ring |4| sealed to the upper plate, and a resilient annular shell |43 sealed to the Vring and Welded to the lower plate. The composite plate |31 consists of a disc |45 of any suitable metal to which a ring-|41 of an alloy suitable .for sealing with glass is welded. The lower plate |39 may be composed of the same metal as the disc |45. A iiat ring |49 of the sealing alloy is welded4 to the upper surface of the shell |43 and sealed to the glass ring |49. Contacts |5| and |53 having an annular form are secured coaxially to the lower plate |39 and the disc |45, respectively. From the center of the lower plate, an insulating pin |55 extends. The pin engages in a notch |51 centrally disposed in the disc |45 and provides a bearing about which the. lower plate' |39 may swivel. 'Ihe container is exhausted `to the same pressure as the containers discussed heretofore.

. .v aseaors The contacts 85| and |53 are spaced a dis-n tance of the order of .l centimeter when disen gaged.. They may be engaged by rotating a peripheral cam |59, the operating surface of which is in engagement with the plate i3d-at a point on its periphery. AS thecam |39 is rotated in a ccunterclockwise direction from the position shown, it raises the plate |39 at one end against the torce of :the resilient shell M33 and the contacts |58 and |53 are engaged. I At the same time, the plate swivels about the point of engagement of the pin and the disc |455, andat the opposite end the shell M3 is opened and the distance between the upper and lower plates is increased. The decrease, in volume eifected on the closing of the contacts |5| and |53 at one end of the container |35 is, therefore, compensated by the opening of the shell at the other end, and the total volume within the ccntainer remains constant.

ln the modification shown in Figs. l0 and il, the xed contact ||3| is disposed along a portion of the inner surface of a anged metallic cup |63. The cup |33 is closed by a Sylphon |635 which is welded to the iiange |69?. The Sylphon |95 is provided with a central opening bounded by an inwardly extending beveled surface |59 to which an annular beveled plate |l| of a glasssealing alloy lswelded. An insulating cylinder H3 is sealed to the alloy plate |l| and. 'a rod mi carrying a metallic cylindrical block llt at its lower end is sealed through the insulator in such manner that the block yextends into the cup |33. The rod is composed or" the sealing alloy and is secured in any suitable manner to the block. The block |15 has a dat portion |l-l in the region of the xed contact ||i|, so that the region of engagement of the block and the.`

contact is a surface of substantial area. The container formed by the -cup |33 and the Sylphon |35 is evacuated in the same manner as in the other modifications of my invention.

A cavity H9 having the cross-section of an arch is provided in the block |15. The cavity is symmetric about the axis of the block and extends from its base along a substantial portion of the length of the block. An Ainsulating pin '|9| fixed centrally 'in the base of the cup |63 extends into the cavity |19 and engages the block |15 at the apex of the cavity. The pin |8| thus constitutes a pivotal'bearing for the block.

The block |15 is pivoted so that the surface |11 engages and disengages the contact I6! by rotating a peripheral spiral cam |83 which engages the upper end of the rod |14. When the cam |83 is rotated in a clockwise direction, the rod |14 and the clock |15 are pivoted about the insulating pin |8| in a counterclockwise direction and the contacts are engaged. The pivoting motion causes the Sylphon |65 to be compressed on the left-hand side and tensioned on the right-hand side. The decrease in volume on the left-hand side is thus compensated by a corresponding in- The apparatus comprises a three-phase trans- I former |89 having a star-connected primary |9| Aminals, each of the phase windings of the secondary sections |95 and |91 are each connected through a readily saturable choke 201 to a brush Y203 which engages a conducting slip ring 205.

'Ihe choke is so designed that it becomes saturated when the current now through it is small compared to the load current. In practice, the saturating current for the choke should be of the order of 1 ampere.

'I'he slip rings 205 are each connected to an insulated segment 209 of one or the other of a pair of commutators 2| The segments 209 are uniformly spaced around the periphery of the commutators 2| each commutator having three 120 segments. The commutatore 2|| and the slip rings 205 are rotated together from a synchronous motor 2|3 which is supplied from the delta secondary section |93. With each commutator 2|| a pair of oppositely disposed brushes 2|5 is associated. Each brush associated with one commutator is conductively connected to a corresponding brush associated with the other commutator. l

`The brushes 2|5 are of compositev structure, each comprising a block 2|1 of conducting material to which an angle 2| 9 of sheet metal is secured. One surface of the block 2| 1 engages the segments 209 as the corresponding commutator`2l| is rotated. One side 22| of each angle Y 2|9 is secured to a surface of the block 2|1 which is perpendicular to the engaging surface in a position such that the other side 223 extends substantially parallel to the segment surface in the region of engagement a short distance frm the segments. The angles`2|9 are so positioned at the block 2|1 that the end of a receding commutator segment 209 passes under side 223 after it passes the block.

The moving parts of the system including the motor 2|3l the slip rings 205, and the segments 209 are disposed in a container 225 within which a pressure of the order of one centimeter of mercury is maintained.' The container may be permanently exhausted or it may be continuously pumped. The supply conductors for the motor and the connecting conductors for the brushes 203 are introduced in the container through eyelets 221. vEacheyelet comprises a central glass plug 229, through which the conductors are sealed and an outer alloy ring 23| is sealed to the glass and welded to the adjacent wall of the container 225.

Ihe commutator brushes 2 |5 are so positioned relative to the segments 209 that the junction region between two segments passes under a brush when the potential of the secondary winding to which one of the segments is connected is passing from a magnitude smaller than the potential of the secondary windingv to which the other segment is connected to a magnitude greater than this potential. At this point the connection to the brush is transferred from one of the receding windings to the approaching winding and the current flow through the brush and lthe receding segment falls to zero, while the current flow through the other segment rises from zero to a predetermined value.. For rectiilcation, that is, where the direct current conductors |81 constitute the Aload and the alternating current conductors constitute the source, the system is adjusted for under commutation in accordance with the preferred practice of my invention. In this case the potential of the receding and the .approaching windings become equal after the block 2| 1 disensages the receding segment and the current zero occurs when the receding segment is passing under the angle 2|9. An arc is ignited between the receding segment 209 and the angle 2 I9 when the brush first disengages the segment since its potential still predominates over that of the approaching segment and as the current zero is approached and passed, the arc is extinguished. The pressure within the container 225 is the same as in the previously described embodiments of the invention and is preferably 'of the-order of 1 centimeter of mercury, and

consequently the brushes 2|9 and the segments 209 are not deleteriously affected by the arcs. The situation is materially improved by the oper- :ation of the chokes 201 which are unsaturated when the commutation occurs, and therefore, absorb a substantial portion of the potential tending to maintain the arc.

Of course', in view of the fact that the current intensity in the arc is small because of the low pressure in the container, the chokes need not in all cases be utilized- In many situations, moreover, a relatively inexpensive choke may be used Where a relatively expensive choke would be required in a conversion arrangement constructed in accordance with the teachings of the prior art.

In Fig. 14, a modification of my invention is illustrated. In this case the brushes are replaced by a circular ring 233 which is tangential to the segments 209. The tangential ring 233 functions as a. brush, and when one segment is being disengaged and the succeeding segment is being engaged, the arcing takes place between the circular ring and the receding segment,

As described herein, the containers involved in the various modifications of my invention are merely exhausted until the desired pressure is attained. Improved operation is attained if the residual gas in the containers is xenon. If the improvement is desired, the containers may be first exhausted and treated to produce aghigh vacuum and then the necessary quantity of xenon may be introduced. i

A divisional application Serial No. 467,761 was jiled December 3, 1942, to cover the embodiments of the invention shown in Figs, 12-14.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

l. A circuit interrupter comprising a confined fluid medium, a vacuum-tight container having a pressure of from about oneto ten centimeters of mercury therein disposed in said medium, cooperative contacts disposed in said container and means for compressing and relaxing said fluid medium to engage and disengage said contacts.

2. A circuit interrupter comprising a confined fluid medium, a plurality of vacuum-tight containers each having a pressure of from about one to ten centimeters of mercury therein disposed in said medium, cooperative contacts disposed in each of said containers, means for connecting the contacts of said containers in series and means for compressing and relaxing said medium to posed. in each. of said containers, means for connecting the contacts of said containers in, series Aand means for compressing and relaxing said medium to close and open said contacts simultaneously, the distance between said contacts when they are open being of the order of .1 centimeter.

d. A circuit interrupter comprising a conned uid medium, a plurality of vacuum-tight containers each having atleast one movable wall and a pressure of from about one to ten centimeters of mercury therein disposed in said medium, cooperativecontactsdisposed in each of said containers, said contacts being actuableto engage and disengage by themovement of said movable wall, means for connecting the contacts of said containers in series and means for compressingand relaxing said medium to close and open said contacts simultaneously.

5. A circuit interrupter comprising a confined iiuid medium, 'a plurality of vacuum-tight containers each having at least one resilient movable Wall and a pressure of from about one to ten centimetersof mercury therein disposed in said medium, cooperative contactsdisposed in each of said containers, said contacts 'being actuable to engage and disengage by the movement of said movable wall, means for connecting the contacts of said containers in series and means for compressing and releasing said medium to a ec close and 'open said contacts simultaneously.

6. A circuit interrupter comprising a vacuumtight container, relatively movable cooperative contacts disposed in said container between which an arc is initially established and plays with its terminals on said contacts, said contacts being relatively movable into and out .of engagement and having a maximum distance of separation no greater than .2 of a centimeter, and a gaseous medium in said container at a pressure such that the current density at the cathode is substantially a minimum.

7. A circuit interrupter comprising a vacuum' .tight container having'a noble gas therein at a pressure of from one-tenth of a centimeter to ten centimeters of mercury, and arc terminal members disposed in said container and between which asador/i meter of mercury to ten centimeters oi mercury to reduce burning of said arc terminal members,

'said members being Vspaced vapart Va distance no burning oi said arc terminals.

vis

including a movable wall of said container, and a an arc is initially established and plays with its terminals on said members.

8. A circuit interrupter comprising a vacuum tight container having a noble gas thereinat a pressure of the order of one centimeter of mercury, and cooperative contact members disposed in said container relatively movable into and out of engagement and between which an arc is initially drawn and plays with its terminals on said members, said contact members having a maximum distance of separation no greater than .2 of a centimeter.

9. A circuit interrupter for interrupting relatively large values of currents comprising a vacuum tight container, arc terminal members disposed in said container between which'an arc is initially established and plays with its terminals on said members, said container being evacuated to a pressure of from one-half a. centi- 1l. A circuit interrupter for interrupting moderate to relatively large amounts oi current ccmprising a vacuum-tight container having solid arc terminal members therein between which an arc is initially established and plays with its terminals on said members, said arc terminal members being spaced apart a distance no `greater than .2 of a centimeter, and a gas in said container at a pressure oi from one-tenth of a centimeter to ten centimeters of mercury to reduce burning of said arc terminals to 'a very small amount.

12. A 'circuit interrupter comprising a vacuum- 4tight container having cooperative contacts disposed therein between whlch an are is initially drawn and plays with its terminals on said contacts, means for engaging and disengaging said contacts, said engaging and disengaging means gas in. said container at a pressure of from one to ten centimeters o i mercury for reducing burning oi said contacts to a small amount.

d3. A circuit interrupter for interrupting moderate to relatively large amounts of current comprising a vacuum-tight container having relatively movable cooperative contacts disposed therein between which an arc is initially established` and plays with its terminaison said contacts, said `contacts when open being spaced a distance no greater than .2 of a centimeter, and a gas in said container at a pressure' of from one to tenv centimeters of mercury to reduce burning of said contacts to a small amount. l

14. A circuit-interrupter comprising a rigid ele-k ment forming one contact of said interrupter, a resilient element carrying another contact of said interrupter, an insulating member insulating said elements from one another and so connected with them that the region bounded by said elements and member is sealed vacuum-tight against the external space, means formoving said resilient element to open and close said contacts, the contact portions of said contacts when opened under load conditions initially drawing an arc which plays with'its terminals on said contacts, said contacts when open being spaced apart a distance no greater than .2 of a centimeter, and a gas disposed in the region bounded lby said elements and member at a pressure of the order of tween which an arc is initially drawn and plays with its terminals on said members, an insulating spacer consisting of laminations of metal separated by strips of insulation between said Walls, and a gaseous medium at a pressure of from onet`nth of a centimeter to ten centimeters of mercury within said container, said arc terminal members being spaced apart a distance no greater than .2 of a centimeter.

17. A vacuum-tight container having cooperative contact members therein relatively movable into and out oi engagement and between which an arc is initially established and plays with its terminals on said contact members, and a noble gas in said container at a pressure of from onetenth oi a centimeter to ten centimeters of mercury to reduce burning of said contact members, said contact members having a maximum separation no greater than .2 of a centimeter.

- 18. A circuit interrupter comprising a vacuumtight container having at least one movable wall, cooperative contacts in said container actuated to open and closed position by the movement of said wall and between which an arc is initially drawn and plays with its terminals on said contacts, means for moving said wall while maintaining the volume within said container unchanged to actuate said contacts, said contacts when opened being spaced a distance no greater than .2 of a centimeter, and a gaseous medium in said container at a pressure of from one-tenth of a centimeter to ten centimeters of mercury.

19. A circuit interrupter comprising a. vacuumtight container having a movable wall which is pivoted adjacent its center, a fixed contact within said container, a movable contact within said container actuated to engage and disengage said iixed contact by the movement of said wall, and means for applying -a force to said wall at a point spaced from the pivot point for moving said wall to actuate said movable contact, said contactswhen opened under load conditions initially drawing an arc which plays with its terminals on said contacts. a gaseous medium in said container at a pressure of from one to ten centimeters of mercury ior reducing burning of said contacts, the contact, portion of said contacts when the contacts are open being spaced a distance no greater than .2 of a centimeter.

20. A circuit interrupter for interrupting moderate to relatively large amounts of current comprising a vacuum-tight container, cooperative contacts in said container relatively movable into and out of engagement, and a gas in said container at a pressure of from one-tenth to ten centimeters of mercury to reduce the arc terminal current density of the arc drawn between said contacts.

JOSEPH SLEPlAN. 

